The present invention relates generally to linkages for connecting a control member to a controlled member.
More particularly, but not exclusively, it relates to an arrangement in which this controlled member consists of a clutch release bearing, i.e. the part usually used for exercising a disengaging function on a clutch, and particularly a motor vehicle clutch, in response to the depressing of the clutch pedal by the driver, the said pedal forming the corresponding control member and being linked to the said release bearing by an appropriate control linkage.
In practice, this control linkage is established between the control pedal and a declutching fork which displaces the release bearing.
In order to reduce the travel of the release bearing in such a way that on contact of the release bearing with the disconnecting means used for disengaging the clutch all noise and wear is prevented from arising, it is customary to subject the declutching fork to elastic means which act on it in a direction in which the release bearing controlled by it is always held applied against the disconnecting means.
Now, as is well known, the friction linings of the clutch disk are inevitably subject to a certain amount of wear during operation which results in an attendant displacement of the disconnecting means and of the release bearing held in contact with these disconnecting means.
If this is not taken into account, and if the length of the control linkage attaching the declutching fork to the control pedal remains constant, the wear of the friction disk results either in a change in the rest position of the control pedal, where this is not determined by a fixed stop, or where a fixed stop is provided, in the untimely appearance of play causing slippage of the friction disk.
In addition, in the case where the control linkage includes a cable, the stretching which such a cable can undergo in service can also lead to opertional problems in the assembly.
In order to reduce these disadvantages it has been proposed to interpose into the control linkage attaching the declutching fork to the control pedal a compensating device to adjust the length of this linkage automatically, and particularly in proportion to the wear of the friction linings.
Such a compensating device is described, for example, in British Patent No. 577,339.
It comprises, on the one hand, two coupling parts which are mounted to move axially telescopically with respect to each other and which are each respectively adapted to be linked in movement to two successive sections of the control linkage concerned and, on the other hand, disconnectable locking means for locking temporarily between them the said coupling parts in an axial direction of movement only.
In this British Patent No. 577,339, however, the disconnectable locking means used consist of balls which are wedged between a cylindrical portion belonging to one of the coupling parts, and a truncated cone portion belonging to the other coupling part.
In practice, therefore, the assembly has to be relatively complex, because there is a requirement for precise surface treatment and processing of the parts, and even then, because of the frictional forces involved and the possibility of marking the portions by the balls working in conjunction with them, correct operation is not assured.
In addition, this arrangement is difficult to implement on already existing installations.
The present invention relates generally to a compensating device for a control linkage of the kind referred to which does not have the disadvantages briefly described above, and which offers other advantages.